Well technology has reached two extremes. Shallow water wells are usually small in diameter, simple and primitive. They involve little more than drilling a hole down to the water table and installing a pump in association with a casing placed in the drilled hole. The hole is seldom more than one hundred feet deep and water simply pours into the hole from the water table. Oil and gas wells are on the other extreme. These wells are often miles deep, are of substantially larger diameter, and are drilled using very expensive and complex technologies, such as diamond tipped drill bits and mud pulse telemetry.
In between these extremes is a field of medium size wells for which technology is largely undeveloped. These medium size wells are typically less than a thousand feet deep (300 m.) and about four inches (10 cm.) in diameter. They reach down to, or below, the water table and have a variety of uses. Some are simply deep water wells. Environmental wells normally fall into this category as well. Environmental wells are used to monitor sub-surface ground water conditions. For example, at a sanitary landfill, environmental wells may be used to monitor contaminants entering the water table or to monitor or vent sub-surface accumulations of methane gas.
Completing an environmental well requires three steps, drilling, development and pumping. In drilling, the well is drilled into a formation using known techniques and a perforated casing, normally made of steel, stainless steel or polyvinylchloride (PVC) is placed in the drilled well to secure the walls. A gravel pack is often placed between the casing and the formation to filter whatever fluids seep or flow into the well from the formation and to stabilize the formation material around the casing.
Development must be done both initially and as a matter of periodic well maintenance. In development, the well is cleaned of loose formation and mud particles and other unwanted residue, and the gravel pack surrounding the well casing is cleaned and settled.
Air surging, in which high pressure air is blasted into the well, is a common method of development but it tends to drive the finer grained particles back into the gravel pack, clogging both the gravel pack and sealing off the formation material, thus reducing the water production of the well.
Surge blocks, which are essentially plungers reciprocated within the well, are also used. When driven up and down within the casing, the surge block forces fluid in the well back and forth through the casing perforations and the gravel pack, and such flow tends to rinse the gravel pack. However, a surge block is effective only when combined with bailing to remove the dirtied liquid out of the well. Bailing involves the use of equipment different from a surge block. The well must be first surged, then bailed, then surged, then bailed and so on, until the well is sufficiently developed. This is very time consuming, especially in deep wells. None of these development techniques allow any control over where within the well the development is occurring.
The third step is pumping in which the ground water and contaminants, or whatever else the well produces is pumped out of the well.
The development process, which must be periodically repeated, is presently expensive and time consuming given the size of these intermediate size wells. Equipment developed for oil and gas drilling is too complex to be useful or cost effective for medium size wells, and equipment developed for water wells is too large and primitive to accomplish the job. Therefore, there is a need for practical and effective development tools specifically suited to medium sized wells like environmental wells.